Switching device for measuring electrical currents and voltages

ABSTRACT

A switching device is used for measuring electrical voltages and/or currents or their differences, particularly for measured values produced in the photometry from tests and comparative tests. The invention is particularly characterized in that values which are to be measured or compared are transformed into a sequence of impulses consisting of impulses following each other alternately in time sequence and having amplitudes corresponding to the measured values. The sequence of impulses, possibly after amplification, is further treated in two separate channels. The treatment consists in that when an impulse of the sequence is present which corresponds to one measured value in one or the other channel, the potential of the impulse sequence in that channel is shifted in the same direction by the corresponding amplitude value. The impulse sequences thus shifted are transmitted to a difference former.

United States Patent Tchang 1 Sept. 25, 1973 [5 1 SWITCHING DEVICE FORMEASURING 3,482,115 2/1969 Kahn et a1. 328/145 X ELECTRICAL CURRENTS ANDVOLTAGES 3,508,158 4/1970 Marchese 328/147 X 3,579,125 5/1971 Lindbladet a1 307/235 X Primary Examiner.lohn W. Huckert Assistant Examiner-L.N. Anagnos Att0rneyV. Alexander Scher et al.

[57] ABSTRACT A switching device is used for measuring electricalvoltages and/or currents or their differences, particularly for measuredvalues produced in the photometry from tests and comparative tests. Theinvention is particularly characterized in that values which are to bemeasured or compared are transformed into a sequence of impulsesconsisting of impulses following each other alternately in time sequenceand having amplitudes corresponding to the measured values. The sequenceof impulses, possibly after amplification, is further treated in twoseparate channels. The treatment consists in that when an impulse of thesequence is present which corresponds to one measured value in one orthe other channel, the potential of the impulse sequence in that channelis shifted in the same direction by the corresponding amplitude value.The impulse sequences thus shifted are transmitted to a differenceformer.

8 Claims, 2 Drawing Figures [75] Inventor: Gabriel A. A. Tchang,Stockholm,

Sweden [73] Assignee: Siemens Aktiengesellschaft,

Erlangen, Germany [22] Filed: Nov. 22, 1971 [21] Appl. No.: 200,694

[30] Foreign Application Priority Data Dec. 5, 1970 Germany P 20 59924.0

[52] U.S. C1 328/105, 307/235 R, 307/242, 307/269, 328/147, 328/153 [51]Int. Cl. H03k 5/18, 1-103k 5/20 [58] Field of Search 307/235, 232, 240,307/242, 243, 261, 265, 268, 269, 271; 328/63, 75, 104, 115-117, 119,135, 145, 147-149, 150, 152, 154; 324/123 [56] References Cited UNITEDSTATES PATENTS 3,278,851 10/1966 Damon, Jr. et a1. 307/235 A X 2,762,9789/1956 Norton 328/148 X 3,076,144 l/1963 Blasbalgm. 328/147 3,076,9332/1963 Negrete 328/147 X 3,219,842 11/1965 Greunke et al.. 307/2353,255,417 6/1966 Gottlieb 328/145 3,387,222 6/1968 Hellwarth et al.307/235 X ACTUATING DEVICE 10 5 13 SWITCH- OVER MEMBER LOGARITHMICAMPLIFIER Patented Sept. 25, 1973 ACTUATING DEVICE SWITCH- OVER 2Shoots-Shoot KEY GIVER U2 FLIP- FLOP )TAGE FLIP- FLOP STAGE DEVICEMEMBER I II LOGARITHMIC AMPLIFIER Fig.1

mes- 17 Patented Sept. 25, 1973 v 3,761,827

2 Sheets-Sheet 1..-

L[ l m Fig.2

SWITCHING DEVICE FOR MEASURING ELECTRICAL CURRENTS AND VOLTAGES Thisinvention relates to a switching device for measuring electricalvoltages and/or currents, or their differences, particularly formeasured values produced in the photometry from tests and comparativetests.

Measuring currents produced in photometry are in the range of tenths ofmicroamperes. There small currents can be amplified and then compared.However, the outlets of switches used for this purpose do not producethe desired measured values in sufficient precision, since the measuredsignals after amplification mostly disappear due to errors oroscillations of amplifiers used for the individual measured values.

An object of the present invention is to improve existing constructionsthrough the provision of a switching device by means of which it will bepossible to measure and compare with sufficient precision even the smallcurrents of the type used in photometry.

Other objects of the present invention will appear in the course of thefollowing specification.

In the accomplishment of the objectives of the present invention it wasfound desirable to transform the values which are to be measured orcompared into a sequence of impulses consisting of impulses followingeach other alternately in time sequence and having amplitudescorresponding to the measured values. The sequence of impulses, possiblyafter amplification, is further treated in two separate channels, inthat when an impulse of the sequence is present which corresponds to onemeasured value in one or the other channel, the potential of the impulsesequence in that channel is shifted in the same direction by thecorresponding amplitude value. The impulse sequences thus shifted aretransmitted to a difference former.

Thus in accordance with the present invention small measured signals canbe changed in a single common amplifier into easily treatable values, sothat all mistakes are eliminated in the following difference formation.The measuring safety of the suggested switching arragement is very highalso for the reason that the sequence of impulses of the impulsescorresponding to individual measured values can be selected to becomparatively high (for example, 1 kH so that even quick changes ofmeasured values can be securely absorbed.

However, the subject of the present invention can be used advantageouslynot only for measuring small electrical signals, but can be alsoeffectively employed in cases where the measured values are only ofshort duration. The switching device of the present invention greatlysimplifies the comparision of measured values appearing for only a shorttime, so that it attains measuring safety which is considerably betterthan that of prior art methods.

In accordance with an advantageous embodiment of the present invention aswitch member actuated by a key giver is used to produce the sequence ofimpulses, the switch member keying the measured in time sequencealternately one after the other. The key frequency of the key giver canbe adjusted. Thus the-obtained frequency can be adapted in a simplemanner to the measuring problem on hand and the speed of variations ofthe measured values can be taken into consideration. For measuringphotometric values in case of sults. Disturbing voltages taking placeduring the pulse pauses have no significance since they areautomatically eliminated in the following difference formation in thedifference former.

According to a further development of the present invention a separateinlet condenser is provided in the channels for supplying the impulsesequence. Furthermore, each channel is provided with a change-overswitch connected behind the corresponding inlet condenser and set to thezero line potential of the impulse sequence. An actuating device is alsoprovided which switches a change-over switch when an impulse derivedfrom a first measured value is present and which switches the otherchange-over switch when an impulse derived from a further measured valueis present so as to connect the zero line potential to the correspondingchannel. The proper actuation of the change-over switches by theactuating device can take place not only on the basis of a program setin time and operated by the key giver, but also by means of actuatingsignals which are derived from the impulse sequence itself, for example,by means of peak detectors. However, when the key giver is used for theoperation, the proper adaptation of the operating signals actuated bythe changeover switches to the corresponding impulses derived from themeasured values is considerably simplified.

The invention will appear more clearly from the following detaileddescription when taken in connection with the accompanying drawingsshowing by way of example only, a preferred embodiment of the inventiveidea.

In the drawings:

FIG. 1 is a diagram illustrating the main circuit of the device of thepresent invention.

FIG. 2 is a diagram illustrating the passage of the voltages appearingat the important parts of the main circuit.

FIG. 1 shows that measured values I and II produced, for example, inphotometry from a test and a comparative test, are transmitted to aswitch-over member 1 which transforms the measured values into animpulse sequence consisting of impulses following each other alternatelyspaced in time and having amplitudes corresponding to the measuredvalues. The impulse sequence thus produced is amplified in a logarithmicamplifier 2 and has the shape of voltage U in FIG. 2, whereby theimpulse I is derived from the measured value I and the impulse II isderived from the measured value II. Thus the member 1 is an ordinaryswitch-over device which in rhythm of the measure producer alternatelyconnects the inlets I or II to the inlet of the amplifier 2.

The impulse sequence U is supplied to the inlet condensers 3 and 4 ofthe two treating channels 3' and 4' the electrodes of which, which arenot connected with the outlet of the amplifier 2, can be switchedalternately over field effect transistors 5 and 6 operating aschange-over switches directly to the zero line potential of the impulsesequence U (mass) or to the high ohmic non invertable inlets of anoperation amplifier 7 or 8. The time periods during which the electrodesare directly connected with the mass, are fixed by opening impulses Uand U produced by an actuating device 9, for the transistors 5 and 6.During the switch-over the condenser electrodes remain connected withthe amplifiers 7, 8. The devices 9 and 10 are producers of switchimpulses, such astransistor switches.

A further operational amplifier 11 is connected behind the operationalamplifiers working as impedance changers. The amplifier 11 forms thedifference between the actual outlet voltages of the amplifiers 7 and 8.The actual present differential voltage is supplied to a closingoperational amplifier 12 working as voltagecurrent changer and istransmitted to an indicating device 13 for indicating purposes.

The switching elements 17 to 23 are NAND gates which apply voltageimpulses produced by a key giver 14 as well as by two flip-flop stages15 and 16 to actuating signals for the proper actuation of theswitch-over device 1 on the one hand and, on the other hand, to theactuating device 9, 10 for the change-over switches 5 and 6.

The operation of the device of the present invention as illustrated inFIGS. 1 and 2 is as follows:

The key giver 14 produces outgoingimpulses U (t) (impulse frequencybeing, for example 1 kH which are changed by the flip-flop stages 15 and16 into impulse sequences U (t) to U (t). The key giver 14 is a normalvoltage impulse producer, for example, an astable multivibrator. Bycombining voltages U, to U in the NAND gates 17 to 19, voltages areproduced at the outlets of members 18 and 19 the running of whichcorresponds to the curves U (t) and U (t) shown in FIG. 2.

The voltages U and U then actuate the switch-over member 1 in suchmanner that every time during the time period while the voltage U iszero, the switchover member 1 is switched to the measuring voltage I andthus during this time period the corresponding measuring value I istransformed into an impulse (I) having an amplitude corresponding to themeasured value. Correspondingly, when the voltage U passes through zerothe switch-over member 1 is switched to the measured value II and duringthat time period an impulse (II) is produced with an amplitudecorresponding to the measured value II.

Due to the logical combinations of the voltages U, and U to U in themembers 20 to 23, outgoing voltages are produced in the members 22 and23 the time extension of which is provided by impulse sequences U,,(!)to U 0) illustrated in FIG. 2. Every time that the voltage U passesthrough zero, the field effect transistor 6 is opened and every time thevoltage U passes through zero the transistor 5 is open (outgoingvoltages of the actuating device 9, l0 correspond to U U) and U U) inFIG. 2).

Therefore, incoming voltages U and U are produced at the non-invertedinlets of operational amplifiers 8 and 17, which correspond to voltagecurves U 0) and, U,,(!) shown in FIG. 2. Thus the voltages U and U arevoltages which are automatically produced by the alternating switchingof the right electrodes of the condensers 3 and 4 to zero potential bythe switches 5, 6.

The difference voltage U -U thus produced at the outlet of theoperational amplifier 11 is also constant after the appearance of thefirst actuating impulse opening the transistor 5 when the measuredvalues I and II are constant, and it corresponds precisely to thedifference between the amplitudes of the impulses (I) and (II) of theimpulse sequence U (t). When the measured values I and II change, thedifference voltage is changed corresponding to the newly appearingamplitude difference.

There are other switching elements consisting of resistances and diodeswhich are generally used for the dimensioning of operational amplifiersor switch transistors. Since these elements are well known in the artthey are not described herein.

The switching device of the present invention is most suitable not onlyfor measuring a single voltage or current (where reference valuecorresponds to the zero potential), but also for measuring thedifference between two voltage or current values. By correspondinglychanging the switching arrangement or the operating program, it ispossible, if necessary, to examine more than two different voltages orcurrents. Then the number of operating channels can be increasedcorresponding to the number of voltages or currents to be treated,whereby all channels will be compared with each other in timely sequenceby a corresponding program actuation. However, it is also possible toleave the two channel system and use a corresponding program actuationto supply only the measured impulses which are to be compared to the twochannels, while the remaining ones are suppressed at the channel inlet.

I claim:

1. A device for measuring the difference between electrical voltages orcurrents derived from measured values, particularly in photometry, saiddevice comprising transforming means transforming values which are to becompared into a single sequence of impulses consisting of impulsesfollowing each other alternately in time sequence and having amplitudescorresponding to the measured values, amplifying means connected to theoutput of said transforming means for amplifying said sequence ofimpulses, and circuit means connected to the output of said amplifyingmeans, said circuit means comprising two separate treating channels forsaid sequence of impulses and a potential shifting device connected toeach of said treating channels for shifting the potential of the wholeimpulse sequence in the one treating channel each time when an impulsecorresponding to the one measured value is presented in said one channelto one direction by an amount corresponding to the amplitude of said oneimpulse and otherwise for shifting the potential of the whole impulsesequence in the other treating channel each time when an impulsecorresponding to the other measured value is presented in said otherchannel to the same direction by an amount corresponding to theamplitude of said other impulse, and a difference former, connected tothe outputs of that treating channels for producing the differencebetween the amplitudes of the so shifted one and other impulse sequence.

2. A device in accordance with claim 1, wherein each treating channelconsists of an inlet condenser connected in series to the output of saidamplifying means,

and a high-ohmic impedance operational amplifier connected in serieswith said inlet condenser and wherein said potential shifting devicecomprises switching means connected to a point in the electrical linebetween said condenser and said high-ohmic impedance operationalamplifier and being adapted to set the zero line potential to said pointand further comprising a switch actuating device connected with theswitching means of each channel and operable to switch the switchingmeans of said one channel to connect the zero line potential to said onechannel when an impulse derived from said one measured value appears insaid one channel and to switch the other switching means of said otherchannel to connect the zero line potential to said other channel when animpulse derived from said other measured value appears in said otherchannel.

3. A device in accordance with claim 1, wherein said transforming meanscomprise a switch-over device and a multivibrator clock connected withand actuating said switch-over device, said switch-over devicealternately testing the measured values one after the other.

4. A device in accordance with claim 3, wherein said transforming meansfurther comprise means adjusting the clock frequency of said clock, saidfrequency for measuring photometric values being in the range of kH 5. Adevice in accordance with claim 4, wherein the ratio between pulseduration and pause duration is greater than one, preferably 3:1.

6. A device in accordance with claim 5, wherein the duration of impulsescorresponding to individual measured values is the same.

7. A device in accordance with claim 1, wherein in the case ofphotometry said amplifying means consists of a logarithmically operatingamplifier.

8. A device in accordance with claim 3, wherein said switch actuatingdevice is connected with and operated by said clock.

1. A device for measuring the difference between electrical voltages orcurrents derived from measured values, particularly in photometry, saiddevice comprising transforming means transforming values which are to becompared into a single sequence of impulses consisting of impulsesfollowing each other alternately in time sequence and having amplitudescorresponding to the measured values, amplifying means connected to theoutput of said transforming means for amplifying said sequence ofimpulses, and circuit means connected to the output of said amplifyingmeans, said circuit means comprising two separate treating channels forsaid sequence of impulses and a potential shifting device connected toeach of said treating channels for shifting the potential of the wholeimpulse sequence in the one treating channel each time when an impulsecorresponding to the one measured value is presented in said one channelto one direction by an amount corresponding to the amplitude of said oneimpulse and otherwise for shifting the potential of the whole impulsesequence in the other treating channel each time when an impulsecorresponding to the other measured value is presented in said otherchannel to the same direction by an amount corresponding to theamplitude of said other impulse, and a difference former, connected tothe outputs of that treating channels for producing the differencebetween the amplitudes of the so shifted one and other impulse sequence.2. A device in accordance with claim 1, wherein each treating channelconsists of an inlet condenser connected in series to the output of saidamplifying means, and a high-ohmic impedance operational amplifierconnected in series with said inlet condenser and wherein said potentialshifting device comprises switching means connected to a point in theelectrical line between said condenser and said high-ohmic impedanceoperational amplifier and being adApted to set the zero line potentialto said point and further comprising a switch actuating device connectedwith the switching means of each channel and operable to switch theswitching means of said one channel to connect the zero line potentialto said one channel when an impulse derived from said one measured valueappears in said one channel and to switch the other switching means ofsaid other channel to connect the zero line potential to said otherchannel when an impulse derived from said other measured value appearsin said other channel.
 3. A device in accordance with claim 1, whereinsaid transforming means comprise a switch-over device and amultivibrator clock connected with and actuating said switch-overdevice, said switch-over device alternately testing the measured valuesone after the other.
 4. A device in accordance with claim 3, whereinsaid transforming means further comprise means adjusting the clockfrequency of said clock, said frequency for measuring photometric valuesbeing in the range of kHZ.
 5. A device in accordance with claim 4,wherein the ratio between pulse duration and pause duration is greaterthan one, preferably 3:1.
 6. A device in accordance with claim 5,wherein the duration of impulses corresponding to individual measuredvalues is the same.
 7. A device in accordance with claim 1, wherein inthe case of photometry said amplifying means consists of alogarithmically operating amplifier.
 8. A device in accordance withclaim 3, wherein said switch actuating device is connected with andoperated by said clock.